1. Field of the Invention
The present invention relates to an apparatus for a High Power Amplifier (HPA) in a wireless communication system. More particularly, the present invention relates to an apparatus for an HPA which obtains optimal performance by controlling a gate bias input to a drive amplifier and a main amplifier according to temperature.
2. Description of the Related Art
A High Power Amplifier (HPA) used in a conventional wireless communication system includes a drive amplifier (hereinafter “amplifier” will also be referred to as “amp” for short) 111 and a main amp 113 as shown in FIG. 1. As also shown in FIG. 1, gate biases 101 and 103 and drain biases 105 and 107 are respectively applied to the drive amp 111 and the main amp 113 so as to amplify the voltage or power of an input signal. In the conventional system, the gate biases 101 and 103, as well as the drain biases 105 and 107, are fixed. In general, the fixed gate biases have values that are obtained by performing an aging operation at a room temperature (e.g. between 15 and 25° C.) during development of the HPA. In other words, during the design and development process of the HPA, the gate biases which provide optimal performance such that there is no gain variation during the process of performing the aging operation at room temperature are determined and set as the fixed gate biases.
However, according to a surrounding environment, the HPA may operate in a low temperature condition or in a high temperature condition. Furthermore, there is a standard in which the HPA must be able to perform a normal operation at a temperature between −40 and 52° C. in both indoor and outdoor environments.
Since the gate bias values of the conventional HPA are obtained by performing the aging operation at room temperature, optimal performance can be achieved only when the HPA operates at room temperature. Thus, the optimal performance cannot be achieved in other conditions, such as a low or high temperature condition. That is, when the conventional HPA operates at a low or high temperature condition, the optimal performance cannot be achieved due to the fixed gate bias. As a result, an Adjacent Channel Leakage Ratio (ACLR) and a constellation error become worse, which leads to deterioration in overall system performance.